How do I create a new mail folder?

Make sure your mailboxes and folders are displayed in the mailbox panel window (see this topic). Then:

If you want to create the mail folder at the top level (not within another folder), right-click on "Eudora" in the mailbox panel window, otherwise right-click on the name of the mail folder in which you want to create the new folder. Click "New" on the menu that comes up.

The New mailbox dialog will appear. Type the name of the new mail folder in the "Name the New Mailbox" field. Click on "Make it a folder" to check it. Click OK.

The New mailbox dialog will appear again. This is so you create at least one mailbox within the mail folder. In the "Name the New Mailbox" field, type the name of a mailbox you want kept in this folder. Click OK.

Your new mail folder will appear in the mailbox panel window with the new mailbox name below it.